As a conventional art, such a spring brake chamber A is employed in a braking control system of heavy vehicles, for example, buses, trucks and trailers, and the spring brake chamber A in the conventional art is shown in FIG. 6. In describing the art, reference numeral 1 is a case on one side, reference numeral 2 is a case on the opposite side and both cases 1 and 2 are connected by a connecting case 3. The case 1 on one side has a chamber 1a and a release bolt 4 is arranged at an axial section thereof in the longitudinal direction. The inner section of the case 1 on one side retractably accommodates, in the axial direction, a spring receiving section 6A of a piston member 6 holding a power spring 5. The piston member 6 is configured of the spring receiving section 6A and a cylinder body section 6B. The outer edge of the spring receiving section 6A of the piston member 6 includes a piston cup 7, and accordingly, the spring receiving section 6A is slidably fitted at an inner wall of the case 1 on one side. When the spring receiving section 6A of the piston member 6, a surface 6b on one side being configured in a convex shape, advances to the right direction, the spring receiving section 6A of the piston member 6 engages a concave section of the connecting case 3.
One side of a cylinder body section 6B of the piston member 6 is retractably fitted at a rear surface of a axle centre of the spring receiving section 6A and the opposite side thereof is retractably fitted at a axle center section 3a of the connecting case 3. Reference numeral 8 is a clamp ring, which fixes the case 2 on the opposite side and the connecting case 3 with the presence of a diaphragm 9. Thus, the case 2 on the opposite side has a chamber 2a and a push rod member 12 is disposed in the chamber 2a. The diaphragm 9 moves to the right direction while compressing a boot 10 and a return spring 11 due to the approaching of the cylinder body section 6B of piston member 6 to the right direction.
The spring brake chamber A performs operations described below. Specifically, a brake pedal as a service brake is stepped on and thereby air pressure instructed from dual brake valves operates a relay valve and the compressed air enters from a service brake port (not shown) of the spring brake chamber A. Thus, air pressure is applied to a pressure chamber 3A (a chamber on the opposite side) of the connecting case 3 and the diaphragm 9 moves to the right direction. Accordingly, the boot 10 and the return spring 11 are compressed and a base plate 12a of the push rod member 12 is moved in the direction of the arrow B. A tip 12d connected to a axle section 12b protrudes moving in the right direction. Accordingly, the air pressure is transmitted to a wheel brake attached to the axle. Thus, the sleeve of an expander inside a brake shoe is expanded and the braking operation is performed by the work of the brake shoe.
On the other hand, when the parking brake is operated, the compressed air is released from the spring brake port (not shown) of the spring brake chamber A and the power spring 5 inside the case 1 on one side is extended, and the spring receiving section 6A and the cylinder body section 6B of the piston member 6 are moved in the direction of the arrow C. Thus, while the spring receiving section 6A is inserted in a chamber 3B on one side of the connecting case 3, the cylinder body section 6B pushes the diaphragm 9 and the base plate 12a of the push rod member 12 in the right direction. Accordingly, the boot 10 and the return spring 11 are compressed and thereby the base plate 12a of the push rod member 12 is moved in the direction of the arrow B. The tip 12d connected to the axle section 12b protrudes moving in the right direction. Accordingly, the air pressure is transmitted to the wheel brake attached to the axle. Thus, the sleeve of the expander inside the brake shoe is expanded and the braking operation is performed by the work of the brake shoe.
Here, the push rod member 12 is configured of a base plate 12a, a axle section 12b connected to the base plate 12a and a tip 12d screwed to a central axle hole 12c of the axle section 12b. The base plate 12a, the axle section 12b and the tip 12d are separated parts respectively and all made of a steel material.
Next, the order of assembling the spring brake chamber A is described in detail based on FIG. 6. A spring seat 1d is inserted in an inner bottom section 1c of the case 1 on one side, from an opening section of the right end 1b of the case 1 on one side and as shown in FIG. 6, a plurality of bolts 1e are screwed and inserted from a left end surface outer wall 1f of the case 1 on one side and thereby the spring seat 1d is fixed at the inner bottom section 1c of the case 1 on one side. At this time, the cylinder body section 6B, the connecting case 3 and the case 2 on the opposite side are not attached to the case 1 on one side. Thus, the power spring 5 is inserted from the opening section of the right end 1b of the case 1 on one side and thereby contacting with the spring seat 1d, and at the same time, the power spring 5 is accommodated inside the spring receiving section 6A. Thus, as shown in FIG. 6, a male screw section 4b formed on the outer edge of the release bolt 4 is inserted into a through hole 6a perforated at the center of the spring receiving section 6A. Here, a head section 4a of the release bolt 4 forms a circular collar. Thus, an assembly worker grips the head section 4a of the release bolt 4 with their fingers, a tool or the like and the end section 4c of the male screw section 4b of the release bolt 4 is screwed into a female screw section 1g perforated in the spring seat 1d to protrude outside the left end surface outer wall 1f of the case 1 on one side. A lock nut 4d is screwed to the end section 4c of the male screw section 4b and is engaged and fixed to the left end surface outer wall 1f of the case 1 on one side. Thus, the screw section 6c of the cylinder body section 6B in which the head section 4a of the release bolt 4 is inserted is screwed and fixed to the outer edge wall 6d of the through hole 6a of the spring receiving section 6A. Accordingly, the connecting case 3 and the case 2 on the opposite side are assembled sequentially and thereby the spring brake chamber A is completely provided.